The present invention relates to computer network interfacing and switching, and more particularly, to an apparatus and method for cascading multiple multiport network switches to increase the number of ports in a network switching arrangement.
Local area networks use a network cable or other media to link stations on a network. Each local area network architecture uses a media access control (MAC) enabling network interfaces at each station to share access to a medium.
The Ethernet, protocol (IEEE Std. 802.3) defines a half-duplex media access format that permits all stations to access the network media channel with equality. Traffic is not distinguished or prioritized over the media. Each station includes an Ethernet interface that uses carrier-sense multiple-access with collision detection (CSMA/CD) to listen for traffic on the media. Any station can attempt to contend for the channel by waiting a predetermined transmission delay interval after the deassertion of the receive carrier on the media, known as the interpacket gap (IPG) interval. If a plurality of stations have data to send on the network, each of the stations will attempt to transmit in response to the sensed deassertion of the receive carrier on the media and after the IPG interval, resulting in a collision. Hence, a transmitting station will monitor the media to determine if there has been a collision due to another station sending data at the same time. If a collision is detected, both stations stop, wait a respective random amount of time, and retry transmission.
A multiport network switch in a packet switching network is coupled to stations on the network through its multiple ports. Data sent by one station on a network to one or more other stations on the network are sent through the network switch. The data is provided to the network switch over a shared access medium according to the Ethernet protocol. The network switch, which receives the data at one of its multiple ports, determines the destination of the data frame from the information contained within the data frame. The network switch then transmits the data from the appropriate port to which the destination network station is connected.
A single network switch may have a number of 10/100 Mb/s ports, such as 12 ports. The use of a single network switch in the Ethernet network may limit the size and speed of the network. The number of end stations connected to the single network switch is limited by the number of ports of the network switch.
Proposals to increase the size of the network by coupling two network switches together through one of the 10/100 Mb/s ports allow data to be transferred from an end station connected to a first network switch to an end station connected to a second network switch. However, since each of the 10/100 Mb/s ports has a MAC for enabling the network interfaces at each station to share access to the medium, the transmission of data between the two end stations through the length between the network switches is relatively very slow. The data would have to be switched by the first network switch, queued and sent over the shared access medium to the second network switch, switched within the second network switch and queued and sent out the correct port of the second network switch to the ultimate destination end station. Furthermore, the transmission rate at the network interface port is limited by the Ethernet protocol. Even if the connection is through a gigabit port, the transmission rate between the network stations is limited by the use of the MAC and the transmission protocol to 1.0 Gb/sec.
There is need for an arrangement and method for cascading a plurality of multiport network switches of a packet switched network in a manner that does not limit the transmission rate between the network switches, so as to provide an arrangement that more closely simulates a single network switch with an increased number of ports.
These and other needs are met by embodiments of the present invention which provide a packet switched network switch arrangement having first and second packet switching network -O switches. A data connection is provided between the first and second network switches. A controller controls the transmission of data from the first network switch to the second network switch in a continuous stream of data bursts.
One of the advantages of these embodiments of the present invention is the transmission of data between the switches in a continuous stream of data bursts. As stated earlier, according to typical Ethernet protocol, data is sent after waiting a predetermined transmission delay interval after deassertion of the receive carrier on the media, known as the IPG interval. This is due to the shared nature of the transmission medium. Hence, the data is not sent in a continuous stream of data bursts. In the present invention, however, the continuous stream of data bursts provides a much faster transmission of data between the network switches. This fast transmission of data allows the two network switches to effectively serve as a single switch with twice the number of ports as either switch by itself.
The earlier stated needs are met by other embodiments of the present invention which provide a multiport packet switched network switch arrangement comprising a first n-port network switch having an expansion port with a transmit side through which data is transmitted from the first network switch and a receive side through which data is received through which data is received with the first network switch. A second n-port network switch is provided having an expansion port with a transmit side through which data is transmitted from the second network switch and a receive side through which data is received at the second network switch. A first unidirectional expansion bus is coupled between the expansion port transmit side of the first network switch and the expansion port receive side of the second network switch for transmission of the continuous stream of data bursts. A second unidirectional bus is coupled between the expansion port transmit side of the second network switch and the expansion report receive side of the first network switch for transmission of a continuous stream of data bursts.
The use of the unidirectional expansion buses between the expansion ports of first and second network switches provides for fast transmissions of continuous streams of data bursts between the networks switches. Thus, the two end-port network switches may act as a single 2n-port network switch.
The earlier stated needs are also met by another embodiment of the present invention which provides a method of operating an m-port network switch on a packet switch network. The m-port network switch has q network switches, each network switch having n-ports, such that qxc3x97n=m. The method comprises the steps of connecting the networks switches in a circular, serial manner such that data is transferable between the network switches only unidirectionally. It is determined in a first one of the network switches that data is to be transmitted from a selected port of second one of the network switches. The data is retrieved from a memory coupled to the first network switch. The data is then transmitted from the first network switch to the second network switch in a continuous stream of data bursts. The data is then transmitted from the selected port of the second network switch.
This method of operating an n-port network switch arrangement is able to operate at a very fast switching rate since the data transmitted between network switches does not have to be sent on a shared transmission medium and may be sent in a continuous stream of data bursts. Furthermore, since MAC""s are not required controlling the access to the medium between the network switches, the transmission speed is limited only by the clock rate of the expansion ports. For example, if 16 bits are transferred each clock cycle, and the clock speed for transmitting the data between the network switches is 75 MHz, the transmission rate is approximately 1.2 Gb/sec. This number is greater than the 1.0 Gb transmission rate available at the fastest 1.0 Gb Ethernet protocol ports. By changing the clock rate to 83 MHz, as provided in preferred embodiments of the present invention, the transmission rate is increased to 1.33 Gb/sec. Hence, the transmission between the network switches is not limited by the use of MAC""s and a shared transmission medium.
Additional advantages and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the present invention may be realized and attained by means of instrumentalities and combinations particularly pointed in the appended claims.